Simbol describes its process as "zero waste" because it will piggyback on geothermal power plants. Simbol will mine commodity metals from the salty water that gushes up from 10,000 feet below ground as part of geothermal power production.

"With the closure of this new financing, we can complete development of the processes needed to produce lithium from brines and effluent streams, in an environmentally conscious manner," Simbol CEO Luka Erceg said in a statement.

Erceg co-founded the company with engineering director John Conley as both pursued MBAs at Rice University in 2006. They have recruited former geochemists from Lawrence Livermore National Laboratory.

Earlier this year, the Cleantech Forum named the Houston-based start-up the most promising technology of the year.